Rest Potential Research Articles

Pseudocapacitive charge storage via hydrogen insertion for molybdenum nitrides

Early transition metal nitrides are promising materials for use in electrochemical capacitors and as electrocatalysts due to their high electronic conductivities, high surface areas and electrochemical stabilities. In addition to double-layer (electrostatic) charge storage, these materials store charge via a pseudocapacitive mechanism involving charge-transfer reactions. This paper describes electrochemical and in-situ X-ray absorption spectroscopic results that provide important insights regarding the pseudocapacitive charge storage mechanism for molybdenum nitrides in aqueous acids. From analysis of the rest potentials at varying pH values, we concluded that electrons and protons were coupled during charge transfer with a ratio of ∼2 electrons per proton. Cycling the Mo2N electrodes between −0.73 and −0.19 V, the stability window for this material, resulted in the removal of approximately one electron per Mo from a band that was primarily Mo in character. The extended X-ray absorption fine structure spectra indicated minimal changes in the immediate local structure around Mo as the potential was varied. The results are consistent with reversible hydrogen insertion into and extraction from interstitial sites in the Mo2N lattice. Charge storage capacitances in excess of 1500 Fg−1 are predicted for materials with full occupation of these interstitial sites.

Transient chaotic behavior during simultaneous occurrence of two electrochemical oscillations

We have found that a chaotic oscillation transiently appears when two kinds of current oscillations, named oscillation A and oscillation α, occur simultaneously. Oscillations A and α appear during the reduction of H2O2 and S2O8 2− respectively on the Pt electrode. When the electrode potential is stepped from the rest potential to a potential where both the oscillations appear, a period-1 oscillation first appears, and then a period-doubling bifurcation cascade occurs. After that, the transient chaos appears, which is followed by a sequence of mixed-mode oscillations (MMOs). The appearance of the chaotic behavior and the MMOs can be explained on the basis of the reported mechanisms for oscillations A and α. Both the oscillations are caused by an N-shaped negative differential resistance (N-NDR) due to the formation of under-potential deposited H (upd-H), indicating that a positive feedback mechanism works during the simultaneous occurrence of oscillations A and α. On the other hand, negative feedback mechanisms for oscillations A and α include the surface concentration of H2O2 and S2O8 2−, respectively. We can, then, conclude that the combination of the positive feedback mechanism and the two negative feedback mechanisms of different time scales gives rise to the chaotic behavior and the MMOs, which has been verified by numerical simulations.

Interpretation of Negative Resistance Observed in Electrochemical Impedance during Copper Electrodeposition Containing Thiourea

The effect of the thiourea on the electrochemical impedance during copper electrodeposition was investigated using a rotating ring disk electrode. The rest potential of the copper electrode measured in the solution containing thiourea was shifted to less noble due to the adsorption of thiourea. The cathode polarization curve of the copper electrode demonstrated that the current density of the copper electrode decreased remarkably because of an increase in the concentration of thiourea. The Nyquist plot of impedance spectrum in the presence of the thiourea described the capacitive loop, which was related to the time constant of the charge transfer resistance and the electric double layer capacitance, in the high frequency range and a part of the large locus crossing the imaginary axis in the low frequency range. This low frequency locus is related to negative resistance which contributes to “leveler” effect. In order to clarify the negative resistance, the theoretical equations of the Faraday impedance were derived. We proposed the four steps of the copper electrodepostion reactions in the presence of thiourea.

Preparation and characterization of palladium-hydride-coated titanium as a reference electrode for the supercritical carbon dioxide emulsion electrochemical system

This work develops a new reference electrode for the electrochemical system using an aqueous supercritical carbon dioxide (sc-CO2) emulsion solutions. Here, the Watts nickel bath is employed to be the standard testing electrolyte. A porous Pd-coated Ti (denoted as Pd/Ti) electrode is prepared by electroplating, which is subjected to the hydrogen sorption (including adsorption and absorption) reaction in 0.5M H2SO4 for forming a palladium hydride-coated titanium (denoted as PdHx/Ti) electrode. The hydrogen sorption/desorption behavior on Pd/Ti is characterized by cyclic voltammetry and rest potential against time analyses. These results reveal that PdHx/Ti is a reliable reference electrode with a reproducible and stable PdHx potential (longer than 10h) in normal aqueous electrolytes at room temperature. The equilibrium potential of this PdHx/Ti electrode is about 65±15mV (vs. RHE) in the Watts Ni bath. Although the hydrogen desorption rate is enhanced by elevating the solution temperature, all of the results confirm that the in-situ formed PdHx/Ti electrode can be practically utilized as a reference electrode in the Watts Ni bath containing the sc-CO2 emulsion medium.

Electrochemical Investigation of Chalcopyrite Oxidation in Alkaline Solutions

Electrochemical oxidation of chalcopyrite (CuFeS2) was investigated as an attempt to gain a better understanding of its surface oxidation chemistry in alkaline solutions. Rest potential measurements, cyclic voltammetry and chronoamperometry experiments were conducted in the pH range of 7 to 13 to determine the influence of pH, immersion time, and applied potential on the mineral oxidation state. Rest potential was found to increase by immersion time and oxygen content of the solution and decrease by the pH value. Cyclic voltammetry experiments revealed that the mineral oxidation occurs in three stages. Increase of the pH value caused the peaks to shift to lower potentials. The results were confirmed by chronoamperometry experiments.

Flotation of Sulfide Components of Copper Ore in the Presence of n-Dodecane

Influence of n-dodecane aqueous emulsion on flotation of sulfide minerals present in the copper ore from the Legnica-Glogow Copper Basin (LGOM), carried out on the laboratory scale, was investigated. Five flotation experiments performed in the presence of different doses of n-dodecane were conducted and compared. Next, mineral analysis of selected flotation products were conducted and discussed. The best flotation selectivity was obtained for bornite, tennantite and chalcocite using 600 g/t of n-dodecane. In the case of non-copper sulfides, the maximum selectivity was observed for sphalerite and galena. Measurements of the rest potential of copper sulfide conducted to explain the differences between recoveries of each sulfide mineral were performed. It was observed, that with increasing sulfide rest potential, the recovery was decreasing. The study provided information hitherto poorly available in literature on flotation of sulfides from the LGOM area with n-dodecane.

Enhancement of Oxygen Reduction Activity of Titanium Nano-Oxide-Based Electrocatalysts for PEFC Cathode

Development of non-platinum electrocatalyst for oxygen reduction reaction (ORR) is required for commercialization of polymer electrolyte fuel cells. We focused on titanium, which is inexpensive and has large amount of resources. Recently, we found that titanium oxide-based compounds made from titanium-organic complexes with oxidation under low oxygen partial pressure had high ORR activity. In this study, we prepared titanium oxide-based ORR catalysts (Ti-CNOs) by conducting ball-mills in dry process or impregnation method with N-methylpyrrolidone as a solvent. We found that the Ti-CNOs prepared by ball-milling in dry process showed high rest potential and large ORR current density. The highest rest potential of the ORR on the Ti-CNOs was over 1.0 V vs. RHE, indicating that titanium oxide-based catalysts are promising as an alternative ORR catalyst.

Enhancement of Oxygen Reduction Activity of Titanium Nano-Oxide-Based Electrocatalysts for PEFC Cathode

Introduction Development of non-noble metal cathodes as alternative materials of platinum is required for practical application of PEFCs. We focused on the oxide-based compounds of group 4 and 5 metals because of their high chemical stability. We reported that carbonitrides of tantalum, niobium, zirconium and titanium oxidized under low oxygen partial pressure had high catalytic activity for oxygen reduction reaction (ORR) in acidic solution [1-3].Recently, we found that titanium oxide-based electrocatalysts (Ti-CNOs) made from organic titanium complexes with heat treatment under low oxygen partial pressure showed high oxygen reduction reaction (ORR) activity [4].In this study, we prepared two kinds of Ti-CNOs, that is, Ti-CNO(TPPz_NMP) prepared by the impregnation method using N-methylpyrrolidone (NMP) as solvent and Ti-CNO(TPPz_dry) prepared by ball-milling in dry process, and compared them to obtain principle of catalyst design. Experimental Oxy-titanium tetrapyrazino porphyrazine (TiOTPPz) was used as a starting material.TiOTPPz was supported on multi-walled carbon nanotube (MWCNT) as a conductive support by impregnation method using NMP as solvent. The powder was heat-treated at 900oC under N2 containing 2% H2 + 0.05% O2 to prepare oxide-based catalyst powder (Ti-CNO(TPPz_NMP)). TiOTPPz was mixed with MWCNT and the mixture was conducted ball-mill in dry process. The powder with dry ball-mills was also heat-treated under the same condition to obtain Ti-CNO(TPPz_dry).All electrochemical measurements were performed in 0.1 mol dm-3 H2SO4 at 30oC with a 3-electrode cell. A reversible hydrogen electrode (RHE) and a glassy carbon plate were used as a reference and a counter electrode, respectively. As pre-treatment, the potential was scanned 200 cycles from 0.05 to 1.2 V with a scan rate of 150 mV s-1 in O2 atmosphere. Then, the rest potential was measured in O2 atmosphere. Next, the potential was scanned 3 cycles from 0.2 to 1.2 V at a scan rate of 5 mV s-1 in both O2 and N2 atmosphere, and the cathodic current density of 3rd cycle was used for the evaluation of the ORR activity. Results and discussion Figure 1 shows the potential – ORR current density curves and the rest potential of the Ti-CNO(TPPz_dry) and Ti-CNO(TPPz_NMP) which were oxidized 10 h. The ORR current density, i ORR, of the Ti-CNO(TPPz_dry) was larger than that of the Ti-CNO(TPPz_NMP). The rest potential of the Ti-CNO(TPPz_dry) was also higher than that of Ti-CNO(TPPz_NMP).Figure 2 shows the relationship between the rest potential and the |i ORR@0.85 V| of the Ti-CNOs(TPPz_NMP) and the Ti-CNOs(TPPz_dry). Positive correlation was observed. The Ti-CNOs (TPPz_dry) had higher rest potentials and larger ORR current than the Ti-CNOs(TPPz_NMP). The secondary particle size of the Ti-CNOs(TPPz_dry) was smaller than that of the Ti-CNO(TPPz_NMP). Therefore, the precursor prepared by ball-milling oxidized more uniformly due to small secondary particles, resulting that the Ti-CNOs(TPPz_dry) had high ORR activity. The highest rest potential was over 1.0 V vs. RHE. Acknowledgements The authors wish to thank ORIENT CHEMICAL INDUSTRIES CO., LTD for supply of oxy-titanium tetrapyrazino porphyrazine (TiOTPPz), and the New Energy and Industrial Technology Development Organization (NEDO) for financial support. Reference [1] A. Ishihara, et al., J. Phys. Chem. C, 117, 18837 (2013).[2] Y. Ohgi, et al., J. Electrochem. Soc., 160, F162 (2013).[3] K.-D. Nam, et al.,Electrochim. Acta, 55, 7290 (2010).[4] K. Suito, et al., J. Fuel Cell Technol., 12, 130 (2013). [in Japanese]

Possibility of Oxide-Based Electrocatalyst toward Oxygen Reduction Reaction as Non Pt Cathode for PEFC

Introduction Development of non-noble metal cathode is required to commercialize polymer electrolyte fuel cells. We focused on group 4 and 5 transition metal oxide-based cathodes, because of their high chemical stability in acidic media (1,2). We have investigated the possibility of the oxide-based cathodes from two viewpoints such as activity and durability.Regarding the enhancement of oxygen reduction reaction (ORR) activity, we used carbon materials such as deposited carbon derived from starting materials and multi-walled carbon nanotube (MWCNT) to obtain sufficient electrical conductivity. We prepared the oxide-based cathodes with high ORR activity by heat treatment of organic complexes such as oxy-metal phthalocyanine or oxy-metal tetrapyrazino porphyrazine under low oxygen partial pressure. Nano-sized oxide-based compounds were successfully obtained to have high ORR activity.On the other hand, regarding the durability, we prepared the oxide-based compounds without carbon to examine the durability at high potential region.In this paper, we introduce the status of development of the oxide-based cathodes from these two viewpoints. Experimental For the ORR activity, oxy-titanium tetrapyrazino porphyrazine (TiOTPPz) and oxy-titanium phthalocyanine (TiOPc) were used as different starting materials. Multi-walled carbon nanotube (MWCNT) was used as catalyst support. TiOTPPz or TiOPc and MWCNT were conducted ball-mills in dry process. The powder was heat-treated for 0.5~10 h at 900oC under N2 containing 2% H2 + 0.05% O2 to prepare oxide-based catalyst powder. Ti-CNO(TPPz) and Ti-CNO(Pc) were designated oxide-based compounds made from TiOTPPz and TiOPc, respectively. For the durability, TiO2 and Nb2O5 were mixed to conduct dry ball-milling to prepare all oxide-based cathodes. The obtained powder was heat-treated at 1050oC for 40 h under 4% H2 to obtain reduced complex oxide (TixNbyOz) on Ti4O7.All electrochemical measurements were performed in 0.1 mol dm-3 H2SO4 at 30oC with a 3-electrode cell. Slow scan voltammetry was performed at a scan rate of 5 mV s-1 from 0.2 to 1.2 V under O2 and N2 atmosphere. A current density was based on the amount of catalyst powder. Triangular potential cycling between 1.0 and 1.5 V vs. RHE with a scan rate of 0.5 Vs-1 was used as degradation test. During degradation test, the SSV was performed, and the durability was evaluated by degradation rate of ORR current at 0.7 V. Results and discussion Fig.1 shows the dependence of the ORR current at 0.85 V and the rest potential of the Ti-CNO(TPPz) and the Ti-CNO(Pc). Both Ti-CNO(TPPz) and Ti-CNO(Pc) had rutile TiO2 structure. The ORR current at 0.85 V and the rest potential had maximum at oxidation time of 2-3 h. The rest potentials were same behavior between the Ti-CNO(TPPz) and the Ti-CNO(Pc), indicating that the quality of the active sites was almost the same. On the other hand, the ORR current at 0.85 V of the Ti-CNO(TPPz) was higher than that of the Ti-CNO(Pc). This is because the oxide particles of the Ti-CNO(TPPz) dispersed higher than the Ti-CNO(Pc). The starting materials affected the dispersion of the oxide particles.Figure 2 shows the degradation rate of the Ti4O7+TixNbyOz and the Zr-CNO(Pc)/MWCNT (zirconium oxide-based compounds prepared by heat treatment of oxy-zirconium phthalocyanines under low oxygen pressure with MWCNT as support) during triangular potential cycling between 1.0 and 1.5 V vs. RHE. The Zr-CNO(Pc)/MWCNT violently deteriorated. On the other hand, Ti4O7+TixNbyOz maintained ORR activity during degradation test. The durability of Ti4O7+TixNbyOz was much higher than that of Zr-CNO/MWCNT in high potential region. Acknowledgements The authors wish to thank ORIENT CHEMICAL INDUSTRIES CO., LTD for supply of TiOTPPz and TiOPc, and New Energy and Industrial Technology Development Organization (NEDO) for financial support. Reference 1) A. Ishihara et al., J Phys Chem C, 117, 18837 (2013).2) Y. Ohgi et al., J. Electrochem. Soc., 160, F162 (2013) (2013).

Electrochemical Impedance Response of Zn Under Anodic Polarization in Simulated Concrete Solution

An understanding of the corrosion behaviour of the zinc alloy coating when placed in concrete and the characteristics of the corrosion products so formed is fundamental to a full appreciation of the corrosion protection afforded by the galvanizing of reinforcement. Pure Zn was chosen because it simulates well the behaviour of galvanized steel, yielding more reproducible results. The aim of this study was to analyze the electrochemical behaviour of pure Zn in Ca(OH)2 saturated solution (simulating the pore solution of concrete) by means of electrochemical impedance spectroscopy measurements under potentiodynamic anodic polarization tests and scanning electron microscopy. Samples used in this work were zinc (99%) alloy, high-grade reagents and distilled water were used to make the solution of saturated Ca(OH)2, anodic polarization and impedance experiments were carried out on a Biologic SP-300 potentiostat. Before the electrochemical tests the specimens are subjected to an exposure of 1 hour in the test solution, the anodic potential scan (0.1 mV s-1) was performed without stirring the solution, starting from the rest potential (Ecorr) and scanning in the anodic direction to 800 mV and 60 mV, during the scanning of anodic polarization from rest potential to 60 mV under a polarization of 10, 20, 30, 40, 50 and 60 mV, the impedance was measured with a sinus amplitude of 10 mV in a frequency range from 200 kHz to 100 mHz. The impedance spectrum shows changes both shape and magnitude indicating more than one process to take place on the surface of zinc, duo to the gradual formation of two semicircles with the increment of potential. (fig.1) These studies are expected to provide technique for development of a protective passive layer on galvanized coatings prior to their embedding in concrete.

The Stability of Nano-Structured-Thin-Film™ Supported Ir on Pt PEMFC Catalysts Under Rde Simulated Start-up and Shut-Down

The instability of Pt oxygen reduction electro-catalysts is a principle cause of proton exchange membrane fuel cell (PEMFC) performance decline, and the main causes of this instability are load cycling and start-up shut-down (su/sd). The extent of Pt loss is primarily a function of 1) rate of potential change 2) upper potential limit.1 Work by 3M and partners on PEMFCs with Nano Structured Thin Film (NSTF) supported catalysts have shown minute amounts (2 – 10 µg cm2) of Ir added to Pt does not adversely affect Oxygen reduction reaction (ORR) activity and is effective in protecting Pt (loss < 10%) under simulated su/sd condition2 The rotating disk electrode (RDE) can also be used to study the behavior of NSTF supported catalysts.3 Many rotating disk electrode (RDE) durability studies subject candidate PEMFC electro-catalysts to triangular wave potential cycling. Stevens et al. have developed alternative electrochemical techniques to simulate the transient potentials associated with load cycling and su/sd.with the RDE.4Figure 1 shows the potential changes of one su/sd “pulse”, designed to simulate run, idle and rest potential with constant potential holds, and simulate start-up and shut-down with constant current holds. This unique approach allows the upper potential limit to change as the test progresses.Figure 2 shows how ORR activity changes under repeated su/sd “pulses” for various loadings of Ir on NSTF supported Pt (85 µg/cm2). Markers are also colored according to the final potential the constant current hold reaches prior to ORR characterization. The highest Ir loading of 19.1µg/cm2 reaches a stable state, where the ORR activity changes very little after 2500 su/sd pulses. For a lower Ir loading (10 µg/cm2) tested at the same current, the ORR activity continually declines. However for the same Ir loading of 10 µg/cm2 tested at 2/5th the current, ORR activity seems to achieve near stability.The results show an interesting relationship between the stability of Ir on Pt electro-catalysts, and the potential reached by the su/sd simulation current. When potential starts and stays below a threshold of approximately 1.5 VRHE, the Ir-Pt reaches a stable configuration where ORR and oxygen evolution reaction (OER) activity no longer decline. Achieving stability may be more dependant on the potential reached, or the charge delivered, than the Ir loading. Note that for pure Pt tested at a current an order of magnitude lower than the 19.2 µg/cm2 Ir sample, and started at a potential of 1.35 VRHE, ORR activity continued to decline, indicating that stability of the RDE-NSTF catalyst system requires both low (< 1.5 VRHE) potential and the presence of Ir.These results indicate a possibility of indefinitely stable Pt based PEMFC catalysts, and the important role the su/sd potential may play in determining stability of an Ir-Pt electro-catalyst. Work is ongoing to determine Ir loading thresholds for stability.1. A. A. Topalov, I. Katsounaros, M. Auinger, S. Cherevko, J. C. Meier, S. O. Klemm, and K. J. J. Mayrhofer, Angew. Chem. Int. Ed., 51, 12613–12615 (2012).2. R. T. Atanasoski, D. A. Cullen, G. D. Vernstrom, G. M. Haugen, and L. L. Atanasoska, ECS Electrochem. Lett., 2, F25–F28 (2013).3. G. C.-K. Liu, R. J. Sanderson, G. Vernstrom, D. A. Stevens, R. T. Atanasoski, M. K. Debe, and J. R. Dahn, J. Electrochem. Soc., 157, B207 (2010).4. D. A. Stevens, J. Harlow, R. J. Sanderson, C. W. Watson, T. J. Crowtz, J. R. Dahn, G. D. Vernstrom, L. L. Atanasoska, G. M. Haugen, and R. T. Atanasoski, ECS Trans., 50, 1533–1538 (2013).

Electrochemical Impedance Study on Dissolution of Cu-Zn Alloy in Fresh Water

The brass (Cu-Zn alloy) is widely used for the water pipe of constructional plant and the joint of the device material. One of the corrosion problems of Cu-Zn alloy is the dezincing, which is the selective dissolution of Zn from Cu-Zn alloy. The fundamental studies of anodic dissolution of Cu-Zn alloy were reported by Pickering et al. (1-3). They indicated that a porous Cu-rich layer was formed on the surface of Cu-Zn alloy due to the preferential dissolution of Zn from Cu-Zn alloy. They proposed the two types of the dissolution mechanisms, which were simultaneous and selective. However, the stability of the Cu-rich layer formed on the Cu-Zn surface has not been clarified yet. In the present study, the dissolution of Cu-Zn alloy in the fresh water was investigated by an electrochemical impedance spectroscopy (EIS). The measurement of the electrochemical impedance was performed by three-electrode system. The working electrode (0.785 cm2) was Cu-Zn alloy (Cu-35at%Zn) and the counter electrode was the platinum wire. The KCl-saturated silver/silver chloride electrode (SSE) was used as the reference electrode. All the potentials in this study were referred to SSE. In order to investigate the stability of the Cu-rich layer formed on the surface of Cu-Zn alloy, the formation of the Cu-rich layer was conducted as follows. The Cu-Zn alloy (Cu-35at%Zn) was abraded by #1200 emery paper under running water. Then, the galvanostatic polarization of Cu-Zn alloy was measured at 1.0 mA/cm2 for 24 h. The electrolyte solution was 0.5M NaCl containing 5mM NaHCO3. The temperature of the electrolyte solution was keep at 60 oC by thermostatic bath. The impedance spectra of the Cu-Zn alloy before and after the formation of Cu-rich layer on the surface of the Cu-Zn alloy were measured to examine the stability of the Cu-rich layer. In addition, the results of the rest potential and the anodic polarization curve were also discussed in the present study. Reference 1. H. W. Pickering and C. Wagner, Journal of the Electrochemical Society, 114, 698 (1967).2. H. W. Pickering, Journal of the Electrochemical Society, 115, 143 (1968).3. H. W. Pickering and P. J. Byrne, Journal of the Electrochemical Society, 116, 1492 (1969).

Action potential initiation in damaged axon initial segment

The effects of physical trauma to nerve cells are of great interest in neuroscience and neuromedicine. The ion channels kinetics are affected by the trauma-induced damage to neural membrane structure. The density of affected channels is at its highest in the nodes and the axon initial segment (AIS). In this study we focus on the consequences of modifying sodium channels kinetics in the AIS to model the effect of damage. It is inspired by a similar study on damaged nodes of Ranvier [1] and by experiments done in vivo on AIS [2,3]. The AIS and the nodes of Ranvier have similar mixtures of channels, but differ in their shapes. Whereas the nodal channels are clustered at high density near a large volume of channel free low capacitance membrane the AIS is long with varying density profiles for each ion channel types. The AIS is the location for action potential (AP) initiation. A neuron was simulated as three sections, each containing multiple compartments: the soma, the initial segment and the myelinated axon. Each compartment was modeled by the classical Hodgkin-Huxley equations using appropriate densities for each type of ion channel. The types of channels and their distributions were based on a previous study looking specifically at cortical pyramidal neurons having Nav1.2 and Nav1.6 at the AIS [4]. The kinetics were modified according to the coupled left-shift (CLS) model [1,5]. This model is based on observations showing that in damaged membranes Na channel kinetic midpoints shift leftward to more hyperpolarized values, effectively rendering the channels hypersensitive. In this study we explore the impact of CLS on the generation of APs in the AIS. The simulation includes NaK-ATPase pumps and inner and outer ion concentrations are monitored. With increased damage, the greater ionic conductance at rest potential (Na-leak conductance) puts greater strain on the pumps. In the case of a single node, hyperexcitability, tonic firing, burst firing, or inexcitability is observed for increasing values of CLS. We explored the effect of damage on the initiation and propagation of APs during repeated stimuli which deplete concentration gradients. Our model allows the investigation of the effect of CLS on the location and duration of the initiation and the threshold duration of Ap-initiatingcurrents. We find that the current threshold for action potential initiation decreases with increased damage or decreased length of the AIS.

Pyrrhotite flotation and its selectivity against pentlandite in the beneficiation of nickeliferous ores: An electrochemistry perspective

Pyrrhotite (Po) is one of the most abundant sulfide minerals in processing industry and must be rejected in most cases. Particularly, Po rejection and its selectivity against pentlandite (Pn) have long been a challenge due to similarities in the mineral composition of the two minerals and the collectorless flotation characteristics of Po. Xanthates have been widely used to promote sulfide mineral flotation; however, in the presence of xanthates, the redox potential established at the mineral/solution interface is most important, determining the flotation performance. In this paper, the importance of electrochemistry in Po and Pn flotation has been demonstrated and a comprehensive study was conducted on two different feed streams (i.e., magnetic concentrate and scavenger cleaner streams, containing magnetic and nonmagnetic forms of Po, respectively), from Vale’s Clarabelle Mill in Sudbury, Ontario, with an objective to determine if improvements in Po rejection and Pn recovery could be achieved by controlling pulp electrochemistry. By conducting a series of flotation tests under different Eh conditions and reagent usage schemes, it was revealed that higher Po content in the magnetic stream may protect Pn from being oxidized, improving Pn recovery. The results indicated that at low oxidizing pulp chemistry, the rest potential for the Pn is still high enough to allow the formation of dixanthogen to promote its flotation. Using a Pt electrode, it was found that by controlling pulp potential at −50<Eh< +50 mV, the Pn recovery and Po depression would be satisfactory. The results, using mineral electrodes (Outotec Chena analyzer), indicated that selective separation can be achieved if low-to-moderate oxidation potentials (0 to 100 mV) or reduction (0 to −100 mV) potentials are monitored using Pn and Po electrodes. Mixing two streams at 50:50 wt % would be possibly beneficial in selective separation.

Comparison between the measured and modeled hydrogen-evolution activity of Ni- or Pt-coated silicon photocathodes

The electrocatalytic behavior of Ni and Pt nanoparticles for the hydrogen-evolution reaction (HER) on p-type Si photocathodes was measured experimentally and the current density vs. potential (J–E) characteristics of a general metal catalyst on p-Si was modeled as a combination of a Si photodiode in series electrically with metal electrocatalysts. Relative to the rest potential, the J–E characteristics produced by the model showed an increase in total overpotential required to reach a specified current density for the metallized photoelectrodes relative to that of a metal electrode. This prediction was in accord with the experimentally observed behavior of Pt on p-Si, but was in contrast to the behavior observed for Ni on p-Si. Properly accounting for junction energetics and kinetics of the HER is critical to accurate predictions of the solar-to-hydrogen (STH) energy-conversion efficiency of metallized integrated photoelectrochemical systems. Further, models that accurately predict the performance of metal catalysts on semiconductor light absorbers are required to optimize the catalytic performance of metallized photoelectrodes.

Analysis of Water Quality for Pitting Corrosion Risk of Copper Used in Heat Exchanger of Air Conditioner

The leakage accident of the water supply pipe and the pipe heat exchanger was the major problem [1, 2], which is attributed to the pitting corrosion of copper. The mechanism of the pitting corrosion of copper has been investigated widely [1-5]. Campbell [1, 3, 4] discussed the occurrence of the pitting corrosion of copper under flowing hard and soft water in the water pipes, indicating that the dissolution of copper was influenced by the water quality significantly.In the present study, the pitting corrosion risk of copper used in the heat exchanger of air conditioner was investigated by the parameters of the water quality sampled by the copper heat exchanger of the air conditioner of all over the country in Japan. The parameters (pH, acid consumption, total hardness) and the concentrations of Cl- and SO4 2- of the sampled water were analyzed to construct two-dimensional phase diagrams. The polarization curve measurement was performed by three-electrode system. The working electrode (0.20 cm2) was the copper plate and the counter electrode was the platinum wire. The KCl-saturated silver/silver chloride electrode (SSE) was used as the reference electrode. The measurement was started from the rest potential to 1.0 V vs. SSE at 100 mV/min. All the potentials in this paper were referred to SSE. The compositions of test solution were determined by the results of the analysis for the sampled water from the copper heat exchanger of the air conditioner of all over the country in Japan. All measurements were made at 25 oC. The results of the two-dimensional phase diagrams and the electrochemical measurement were discussed in this paper.Reference[1] H. S. Campbell, Journal of Applied Chemistry, 4, 633 (1954).[2] V. F. Lucey, British Corrosion Journal, 2, 175 (1967).[3] H. S. Campbell, Water Treatment and Examination, 20, 11(1971).[4] H. S. Campbell, Journal Institute of Metals, 77, 345 (1950).[5] R. May, Journal Institute of Metals, 82, 65 (1953).

Role of copper and aluminum additions on the hydrogen embrittlement susceptibility of austenitic Fe–Mn–C TWIP steels

The role of alloying elements on the hydrogen embrittlement (HE) susceptibility of a Fe–18Mn–0.6C alloy was investigated by in situ tensile tests and characterized by the ductility loss associated with intergranular fracture. Under cathodic polarization an improvement of HE resistance is related to the SFE increase with Cu or Al additions reducing the stress–strain and H localization at grain boundaries, which prevents H-induced intergranular cracking. At rest potential, beneficial effects of Cu and Al are related to their influence on hydrogen absorption during the corrosion process. However, residual phosphorus strongly reduces the beneficial effect of aluminum.

Effect of Pressure, Surface Tension and Rest Potential on Osteo Intra Organelle Nanoporation in an Advanced Micro Chip

We report the effect of pressure, surface tension and rest potential on intra organelle nanoporation of multi layer osteoblast cell placed in a 3D non uniform micro fluidic chip composed of bi metallic heterogeneous micro electrode under the influences of smart control FPGA based Pico pulse generator. It is exposed that all above parameters are not uniformly distributed over the surface and affects the pore free energy. Pore radius and density are symmetric about the equator with the same value at both poles of the cell. In addition, the value of the rest potential and surface tension affect membrane potential around the cell because the electro oration current is several orders of magnitude larger than the ionic current that supports the rest potential and surface tension. Complete resealing to pre shock conditions requires specific surface tension and pressure.

Formation of hydrogen peroxide by sulphide minerals

Formation of hydrogen peroxide (H2O2), an oxidizing agent stronger than oxygen, by sulphide minerals during grinding was investigated. It was found that pyrite (FeS2), chalcopyrite (CuFeS2), sphalerite ((Zn,Fe)S), and galena (PbS), which are the most abundant sulphide minerals on Earth, generated H2O2 in pulp liquid during wet grinding in the presence of dissolved oxygen in water and also when the solids are placed in water immediately after dry grinding. Pyrite generated more H2O2 than other minerals and the order of H2O2 production by the minerals found to be pyrite>chalcopyrite>sphalerite>galena. The pH of water influenced the extent of hydrogen peroxide formation where higher amounts of H2O2 are produced at highly acidic pH. Furthermore, the effect of mixed sulphide minerals, i.e., pyrite–chalcopyrite, pyrite–galena, chalcopyrite–galena and sphalerite–pyrite, sphalerite–chalcopyrite and sphalerite–galena on the formation of H2O2 showed increasing H2O2 formation with increasing pyrite fraction in chalcopyrite–pyrite, galena–pyrite and sphalerite–pyrite compositions. The results also corroborate the amount of H2O2 production with the rest potential of the sulphide minerals; higher rest potential of a sulphide mineral results in more formation of H2O2. Most likely H2O2 is responsible for the oxidation of sulphide minerals and dissolution of non-ferrous metal sulphides in the presence of ferrous sulphide in addition to galvanic interactions. This study highlights the necessity of revisiting the electrochemical and/or galvanic interactions between pyrite and other sulphide minerals in terms of their flotation and leaching behavior in the context of inevitable H2O2 existence in the pulp liquid.

The Influence of Pyrite on Galvanic Assisted Leaching of Chalcocite Concentrates

The dissolution of metal sulfides is controlled by their solubility product and valence bond theory, pyrite and chalcocite have different electronic nature of the valence energy band, with which the electrolyte may exchange electrons during dissolution reaction, so they have different principals of dissolution. Pyrite which has a higher rest potential is galvanically protected, while chalcopyrite which has a lower rest potential is preferentially leached. Pyrite is intentionally added to the leaching of chalcocite concentrates, we investigated the influence of pyrite to chalcocite weight ratio, solution pH , Eh and the presence of bacteria on assisted leaching of chalcocite concentrates. The leaching solution redox potential, pH, iron, copper and bacteria were monitored, leached residue was collected and analysed to understand leaching mechanism. We found that chalcocite leaching efficiency is enhanced with pyrite:chalcocite weight ratio increased.